1. Field of the Invention
This invention relates to combustion driven fastener hand tools. Particularly, this invention relates to a combustion driven fastener hand tools having a control valve between two portions of a combustion chamber.
2. Description of the Related Art
Powered fastener driving tools, e.g. nail guns, have existed for decades. Perhaps not coincidentally, the first commercial nail gun was introduced in 1950 after World War II wherein the technology for rapidly firing projectiles was greatly advanced. The first nail guns were pneumatic, driven by compressed air. Although pneumatic power is still the most prevalent, over time fastener driving tools have been developed using other means of power, such as electric motors, solonoids, combustibles, e.g gas or explosive powder, have also been developed. Some development of technology related to powered fastener drivers, and particularly combustion driven fastener tools has occurred. However, there is still much need for further development.
Combustion driven fastener hand tools employing combustibles, e.g. gas or powder, to force a piston driver against a fastener introduce a unique set of parameters which must be properly balanced in order to achieve a working device. Sizing of the combustion chamber and valving are critical, in addition to the fuel delivery and mixing components. Moreover, greater optimization of a given design to improve power and efficiency can be greatly affected through precise understanding of the combustion process. For example, it has been determined that using a combustion chamber divided into portions having a control plate therebetween can greatly improve the efficiency and power of a combustion driven fastener device. In addition, it has also been previously observed that accurate location of the starting position of the driving piston can be important in the operation of a combustion driven device, particularly if the piston is heavy and likely to move under its own weight.
U.S. Pat. No. 8,925,517, issued Jan. 6, 2015, by Adams, which is incorporated by reference herein, discloses a gas-powered tool motor includes a combustion chamber with an intake valve at one end, an exhaust valve at another end, and a control plate or control valve between two portions of the combustion chamber. A piston or other positive displacement device is in communication with the combustion chamber. The intake and exhaust valves have closure members that are movable along a common axis in tandem between collective open positions for recharging the combustion chamber with the fuel and air mixture and collective closed positions for detonating the fuel and air mixture in the combustion chamber and displacing the positive displacement device. The control plate or control valve supports limited air flows from a first portion of the combustion chamber to a second portion of the combustion chamber even in the closed position of the control valve for supporting two-stage combustion.
Adams teaches use of a control valve between two portions of a combustion chamber having a closure member affixed to a central shaft (which moves axially to open and close the valve) and a control seat and forming a gap therebetween in the closed position. Upon combustion (with the control valve close) in the first portion of the combustion chamber, the flame front moves towards the gap, preferably driving a fuel/air mixture through the gap and compressing the combined fuel/air mixture in the second portion of the combustion chamber just prior to ignition in the second portion of the combustion chamber yielding more power to the fastener driver than would otherwise be elicited from an undivided combustion chamber burning the same amount of fuel.
Alternately, Adams teaches a control valve comprising a spring-loaded poppet having a closure member which moves along a central shaft and has a chamfered edge biased against a mating control valve seat affixed to the combustion chamber wall. The flame front moving through the first combustion chamber portion overcomes the spring bias and opens the valve, preferably driving a fuel/air mixture through the gap and compressing the combined fuel/air mixture in the second portion of the combustion chamber just prior to ignition in the second portion of the combustion chamber. Combustion in the second portion of the chamber then closes the valve.
Adams also discloses use of an alternate control plate affixed to a central shaft (which moves axially to open and close the valve) which forms an anular gap between the plate and the cylinder wall which functions similar to the gap between the closure member and the control seat of the control valve described above. Limited size openings may additionally be made through the control plate to support limited flow through the control plate. In a similar manner, the control plate can alternately be affixed to the cylinder wall allowing a central shaft to move freely through a central orifice of the control plate. In this case, limited flow through the control plate is formed solely by limited size openings through the plate.
The various control valve and control plate embodiments taught by Adams either yield equivalent flow in both directions with the valve in the closed position, i.e. between the closure member and seat or the control plates, or require additional moving parts and complexity, i.e. the poppet valve having a spring and control plate moving on the tie rod, which could limit life of the device being subject to combustion gases. A closed control plate, even one with orifices, as taught by Adams serves to block combustion pressure between the two portions of the combustion chamber.
In view of the foregoing, there is a need in the art for control valve apparatuses and methods for operation between the two portions of the combustion chamber within a combustion driven fastener hand tools. There is a need for such devices to improve efficiency and delivered driving power. There is also a need for such apparatuses and methods that operate reliably and efficiently over many uses and at a reduced cost. These and other needs are met by the present invention as detailed hereafter.